In a paired piston engine each cylinder contains two pistons opposing each other and sharing the same combustion chamber. These two pistons are then working on the same combustion chamber at the same time, reducing the need for a large heavy block. To make this feature work two crankshafts geared together with a central idle gear and shaft are incorporated with the pistons. In different configurations such as two cyliners with four pistons of four cylinders with eight pistons, or diesel or fuel injected, the engine is a potentially light, small, very powerful power plant.
However, the paired piston configuration which has been designed under a four cycle sequence has presented problems unacceptable to the present engine standards. The high rpm of a four cycle approach to obtain equal horsepower increases maintenance costs. Also, because of the rapid expansion of the combustion chamber, due to the larger mixture charge to achieve it, a 4 cycle sequence produces a fuel useage greater than convential cylinders along with an unacceptable emission output.
Rotary valves have been the object of study for many years without success because their design has not accommodated the various environmental problems they encounter. These problems relate to the inability to achieve proper cooling, sealing, lubrication and protection against wear and corrosion.